In the standard serializer for bunyan the req- and res-objects are serialized when creating a child-logger, like

var child = bunyan.child({

req: reqObj,

res: resObj

});

This means that that if the reqObj or resObj get changed after the child has been initated those changes will not be logged properly.
The serializers for req and res-objects are in this project not serialized when a child is created but rather when you actually log.